Use-After-Free Vulnerability in Firefox Browser by Mozilla
CVE-2026-4701

9.8CRITICAL

Key Information:

Vendor

Mozilla
Status
Firefox
Firefox Esr
Thunderbird
Vendor
CVE Published:
24 March 2026

What is CVE-2026-4701?

A use-after-free vulnerability exists in the JavaScript Engine of the Firefox browser, affecting versions prior to 149 and Firefox ESR versions below 140.9. This flaw can potentially allow an attacker to execute arbitrary code or crash the browser, compromising user security. It is critical to update to the latest versions to mitigate risks associated with this vulnerability.

Affected Version(s)

Firefox < 149

Firefox ESR < 140.9

Thunderbird < 149

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2009303
https://www.mozilla.org/security/advisories/mfsa2026-20/
https://www.mozilla.org/security/advisories/mfsa2026-22/

CVSS V3.1

Score:
9.8
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Gary Kwong
.